The present invention relates to a transparent coat layer forming apparatus for forming a transparent coat layer made of transparent toner on a surface of a color image formed by a copying machine or a printer adopting an electrophotographic system, an electrostatic recording system, and the like, or an image forming apparatus such as a facsimile, and a color image forming apparatus using the transparent coat layer forming apparatus.
Conventionally, in the case where a color image is formed on a transfer material in a copying machine or a printer adopting an electrophotographic system, an electrostatic recording system, and the like, or an image forming apparatus such as a facsimile, a color original is copied, for example, as follows. In the image forming apparatus, a color original is set on a color scanner, the color original is illuminated with light, and light reflected from the color original is split to three colors (e.g., RGB) by the color scanner and read. Image data of the color original read by the color scanner is subjected to predetermined image processing by an image processing device. Thereafter, an image signal of plural colors (e.g., Y (yellow), M (magenta), C (cyan), and K (black)) obtained by color correction is sent to an image exposure device on a color basis. Then, in the image forming apparatus, the image is exposed to light based on the image signal of plural colors sent from the image processing device by the image exposure device. In the image exposure device, for example, a laser light source such as a semiconductor laser is modulated, and a laser beam modulated based on the image signal is emitted from the semiconductor laser. The laser beam is irradiated onto an inorganic photosensitive member such as Se and amorphous silicon or an organic photosensitive member using a phthalocyanine pigment, a bis-azo pigment, or the like as a charge generating layer in plural times for each color. Consequently, plural electrostatic latent images are successively formed for each color on a photosensitive drum made of an inorganic photosensitive member or an organic photosensitive member, every time the photosensitive drum is rotated. The plural electrostatic latent images successively formed on the photosensitive drum are successively developed, for example, with toner of four colors (Y, M, C, and K). The first electrostatic latent image is Y, the second electrostatic latent image is M, and the like. Then, the toner images of the respective colors (Y, M, C, and K) successively formed on the photosensitive drum are finally transferred together in an overlapped state onto a transfer material such as a sheet. Thereafter, the toner images of the respective colors transferred together in an overlapped state onto the transfer material are pressurized by heating to be fixed onto the transfer material with a heat-fixing roller or the like. Thus, a color image is formed.
The color toner used in the above-mentioned image forming apparatus is composed of particles containing, for example, binding resin (e.g., polyester resin, an ethylene/acrylic copolymer, and a styrene/butadiene copolymer) in which a colorant is dispersed, and having an average particle size of 1 to 15 xcexcm. Fine particles having an average particle size of about 5 to 100 nm (e.g., inorganic fine particles such as silicon oxide, titanium oxide, and aluminum oxide or resin fine particles such as PMMA and PVDF) adhere to the particles of the color toner. Examples of the above-mentioned colorant will be given below. As the Y (yellow) colorant, for example, benzidine yellow, quinoline yellow, Hansa yellow, and the like are used. As the M (magenta) colorant, rhodamine B, rose Bengal, pigment red, and the like are used. As the C (cyan) colorant, phthalocyanine blue, aniline blue, pigment blue, and the like are used. As the K (black) colorant, carbon black, aniline black, a blend of color pigments, and the like are used.
A color image made of the color toner thus formed has its surface fixed and smoothed by heating when being nipped between a heating roller and a pressurizing roller. Therefore, the color image has glossiness different from that of the surface of a sheet. Furthermore, the viscosity of the color toner is varied during fixing by heating, depending upon the kind of binding resin, a method for fixing by heating, and the like. Thus, it is known that the glossiness of a color image is varied.
The preference for the glossiness of a color image is varied depending upon the kind of an image, the purpose of use, and the like. However, in the case of a photographic original of a person, a scene, or the like, an image with high glossiness is preferred so as to obtain a clear image.
As a technique of obtaining an image with high glossiness by using an image forming apparatus such as a color copying machine, for example, those which are disclosed in JP 5-142963 A, JP 3-2765 A, JP63-259575A, and the like have already been proposed. According to the techniques disclosed in these publications, it is attempted to obtain an image with high glossiness by selecting the material for toner, fixing conditions thereof, and the like.
In the case of the techniques disclosed in these publications, although the glossiness of an image part made of toner can be enhanced, the glossiness of a non-image part composed of a surface of a transfer material cannot be enhanced. Therefore, these techniques have a problem that the glossiness of the surface of a transfer material cannot be enhanced and made uniform. Furthermore, in the case of the, techniques disclosed in the above publications, in an image part made of color toner, the layer thickness of a color toner image is varied depending upon the number of colors of color toner forming the image part. Therefore, the unevenness caused by the difference in layer thickness of a toner image remains on the surface of an image, which prevents the surface of an image from being smooth as in a photograph or printed matter and makes it impossible to obtain smooth texture.
In order to solve the above-mentioned problem, the technique disclosed in JP 3-130791 A has already been proposed. According to the technique disclosed in JP 3-130791 A, a transparent resin layer is formed on a fixing belt, and the transparent resin layer is overlapped to be fixed to a transfer material with a toner image adhering thereto, whereby the glossiness on the transfer material is made uniform.
However, the above-mentioned conventional technique has the following problem. That is, in the case of the conventional technique disclosed in JP 3-130791 A, transparent resin is developed on a photosensitive drum in a contact portion between an apparatus for forming a transparent resin layer and a fixing belt at start-up of an apparatus. The development of the transparent resin on the photosensitive drum is caused by the difference between the charge potential of the photosensitive drum at start-up of an apparatus and the potential of a DC bias of a developing device as shown in FIG. 9. Furthermore, if the transparent resin is developed on the photosensitive drum at start-up of an apparatus, i.e., in the absence of a transfer material, the transparent resin developed on the photosensitive drum is transferred to and accumulated on the fixing belt to some degree due to the absence of the transfer material. As a result, the transparent resin accumulated on the fixing belt is diffused on its periphery to adhere to the reverse surface of a recording sheet and contaminates it. Furthermore, the transparent resin accumulated on the fixing belt is transferred to the surface of the recording sheet in some cases, thereby causing a step or a difference in glossiness.
In order to solve the above-mentioned problem, the inventors of the present invention have studied a configuration in which a photosensitive drum 100 used for forming a transparent resin layer and a fixing belt 101 are retracted from each other while an image is not being formed, as shown in FIG. 10.
However, in the case where the photosensitive drum 100 and the fixing belt 101 are retracted while an image is not being formed as described above, another problem occurs this time as follows. That is, it has been found that due to influences of the very high belt tension (i.e., about 10 kgxc2x7f) for stretching the fixing belt 101, the occurrence of meandering while running the fixing belt 101, and the change in speed of the fixing belt 101 caused by fixing at a very high pressure, the contact between the photosensitive drum 100 and the fixing drum 101 becomes unstable. This prevents the transparent resin layer from being formed on the fixing belt 101 uniformly, and prevents an image with uniform and high glossiness from being formed.
Furthermore, when the leading edge and the trailing edge of a recording sheet 102 pass through the inlet/outlet of a fixing nip portion between fixing rollers 103 and 104, the speed of the fixing belt 101 is fluctuated. This prevents a uniform transparent resin layer from being formed. Furthermore, when the fixing belt 101 and the photosensitive drum 100 for forming a transparent resin layer are driven by separate driving devices, the difference in driving speed necessarily occurs between the belt driving device and the transparent resin layer forming apparatus, as shown in FIG. 11. Due to the difference in driving speed, the fixing belt 101 and the photosensitive drum 100 are subjected to stick-slip, making it impossible to form a transparent resin layer stably. Herein, the term xe2x80x9cstick-slipxe2x80x9d refers to a phenomenon in which the fixing belt is repeatedly deformed minutely and slips. The reason for this is considered as follows. The difference in driving speed between the belt driving device and the transparent resin layer forming apparatus causes a difference in speed between the fixing belt 101 and the photosensitive drum 100. When the difference in speed is caused therebetween, the fixing belt 101 made of an elastic member is deformed elastically. When the elastic deformation force of the fixing belt 101 exceeds the frictional force between the fixing belt 101 and the photosensitive drum 100, the fixing belt 101 slides to slip, whereby the elastic deformation force is removed. Then, due to the difference in speed therebetween, the phenomenon of elastic deformation of the fixing belt 101 is repeated again, whereby xe2x80x9cstick-slipxe2x80x9d occurs.
Furthermore, when the recording sheet 102 passes through the inlet/outlet of the fixing nip portion, the speed of the fixing belt 101 is fluctuated. Therefore, while the recording sheet 102 is passing through the fixing nip portion, an image at the next page cannot be formed. As a result, a transparent resin layer cannot be formed at a high speed.
It is also considered that, in order to reduce the difference in driving speed between the belt driving device and the transparent resin layer forming apparatus, the transparent resin layer forming apparatus is driven so as to co-rotate with (follow) the fixing belt. However, in such a case, as shown in FIG. 12, the frictional force between the fixing belt 101 and the photosensitive drum 100 is varied, depending upon the area of the transparent resin layer formed on the fixing belt 101. Then, the driving of the transparent resin layer forming apparatus including the photosensitive drum 100, following the fixing belt, becomes unstable, making it impossible to form a transparent resin layer uniformly as another problem.
In order to overcome the above-mentioned problem, it is required to decrease a fixing pressure and a speed, and perform driving control with high performance, which causes other problems such as enlargement of an apparatus and a decrease in productivity.
The present invention has been made in view of the above circumstances and provides a transparent coat layer forming apparatus capable of allowing the entire surface of an image to be smooth and uniformly providing high glossiness to a transfer material irrespective of an image density without causing an enlargement of an apparatus and a decrease in productivity, and a color image forming apparatus using the transparent coat layer forming apparatus.
In order to attain this, the present invention provides a transparent coat layer forming apparatus, including:
a heat-fixing device provided with a fixing belt;
a particle layer forming apparatus that forms a particle layer made of transparent toner on the fixing belt of the heat-fixing device;
plural rollers including a transfer roller which stretches a transfer region of the fixing belt to which the particle layer is transferred from the particle layer forming apparatus in a plane shape; and
a retract mechanism that allows the fixing belt stretched in a plane shape by the plural rollers including the transfer roller to contact/separate from the particle layer forming apparatus,
in which the particle layer is formed on the fixing belt by the particle layer forming apparatus, and the particle layer formed on the fixing belt of the heat-fixing device is overlapped with a transfer material with an image transferred thereto in a fixing nip portion, followed by heating and pressurizing, whereby a transparent coat layer made of the particle layer is formed on the transfer material with the image transferred thereto.
The particle layer forming apparatus to be used may be provided with a photosensitive drum, for example.
Furthermore, in the transparent coat layer forming apparatus of the present invention, for example, a speed unevenness absorbing unit is provided, which absorbs a speed unevenness of at least one of the heat-fixing device and the particle layer forming apparatus.
In the transparent coat layer forming apparatus according to the present invention, the speed unevenness absorbing unit includes a unit that is, for example, composed of a one-way gear configuration that is placed in a driving force transmission path of the driving device for the particle layer forming apparatus, is rotated in one direction without a load and locked in rotating in the other direction to transmit a rotation force, is adapted to drive the driving device for the particle layer forming apparatus at a speed slightly lower than that of the fixing belt of the heat-fixing device, is rotated during a normal operation freely without a load to thereby drive the particle layer forming apparatus following the fixing belt, and is locked to transmit the driving force from the driving device to the particle layer forming apparatus when the speed of the particle layer forming apparatus is decreased (in an abnormal state).
Further, in the transparent coat layer forming apparatus according to the present invention, the speed unevenness absorbing unit to be used includes, for example: a detection device that detects a speed of the particle layer forming apparatus; a judging device that judges abnormality based on a detection result of the detection device; and an electromagnetic clutch placed in the driving force transmission path of the driving device for the particle layer forming apparatus, in which the driving force from the driving device for the particle layer forming apparatus is ON/OFF controlled by the electromagnetic clutch in accordance with a judgement signal from the judging device, whereby the driving force is transmitted to the particle layer forming apparatus.
Further, in the transparent coat layer forming apparatus according to the present invention, the speed unevenness absorbing unit to be used includes, for example, a clutch that brakes rotation at a predetermined speed or more placed in the driving device for the particle layer forming apparatus or the heat-fixing device, thereby decreasing change in speed.
Further, a color image forming apparatus according to the present invention includes:
an image bearing member;
a colored toner developing device that forms insulating colored toner images of at least cyan, magenta, and yellow on the image bearing member;
an intermediate transfer member to which the colored toner images are transferred from the image bearing member;
a first transfer device that transfers the colored toner images from the image bearing member onto the intermediate transfer member;
a second transfer device that transfers the colored toner images on the intermediate transfer member onto a transfer material;
a heat-fixing device having a fixing belt which fixes the colored toner images on the transfer material by heating;
a particle layer forming apparatus that forms a particle layer made of transparent toner on the fixing belt of the heat-fixing device;
plural rollers including a transfer roller which stretches in a plane shape a transfer region of the fixing belt to which the particle layer is transferred from the particle layer forming apparatus; and
a retract mechanism that allows the fixing belt stretched in a plane shape by the plural rollers including the transfer roller to contact/separate from the particle layer forming apparatus,
in which the particle layer is formed on the fixing belt by the particle layer forming apparatus, and the particle layer formed on the fixing belt of the heat-fixing device is overlapped with a transfer material with the colored toner images transferred thereto, followed by heating and pressurizing, whereby a transparent coat layer made of the particle layer is formed on the transfer material with the colored toner images transferred thereto.
Then, in the color image forming apparatus according to the present invention, the particle layer forming apparatus and the fixing belt of the heat-fixing device are driven as described above for instance.
According to the present invention, the above-mentioned configuration includes basically plural rollers including a transfer roller which stretches in a plane shape a transfer region of a fixing belt to which a particle layer is transferred from the particle layer forming apparatus and a retract mechanism that allows the fixing belt stretched in a plane shape by the plural rollers including the transfer roller to contact/separate from the particle layer forming apparatus. Because of this, while the particle layer forming apparatus is exactly in contact with the fixing belt by the plural rollers including the transfer roller for stretching the fixing belt in a plane shape, the particle layer forming apparatus is retracted from the fixing belt when this contact is not necessary. Thus, it is possible to provide a transparent coat layer forming apparatus capable of allowing the entire surface of an image to be smooth and providing high glossiness to a transfer material irrespective of an image density without causing an enlargement of an apparatus and a decrease in productivity, and a color image forming apparatus using the transparent coat layer forming apparatus.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.